Naphthalene in purified form is in substantial demand as an intermediate for a variety of uses, for example, synthetic resins, textile chemicals, tetralin, decalin, etc. Tetralin and decalin are useful as desorbents in chromatographic bulk separations. A readily available source of naphthalene is coal tar distillates or fractions resulting from catalytic processing of petroleum. Normally, purification is accomplished by crystallization and/or distillation of a fraction having a narrow boiling point range and/or melting point, but a large number of theoretical stages is required.
The separation of naphthalene from light cycle oils from catalytic cracking processes by adsorption with activated carbon has been disclosed in U.S. Pat. No. 3,697,414. Carbon adsorbents, however, generally have low capacities and adsorption-desorption rates. To overcome these drawbacks, an adsorbent with higher capacity and faster desorption rates is desired.
U.S. Pat. No. 4,357,276 discloses that indole may be separated from a coal tar fraction containing naphthalene and 2-methylnaphthalene, on X and Y type zeolites exchanged with Group IA cations whereby indole is selectively adsorbed by the zeolite and naphthalene is co-rejected with the other components of the coal tar fraction. Various desorbents are disclosed, but there is no suggestion that the adsorbent-desorbent combination of the invention is capable of selectively adsorbing naphthalene and rejecting other components in the naphthalene mixture.
Eremenko et al, Teor. Eksp. Khim., 5(2), pp 242-6 (1969), have disclosed that naphthalene could be adsorbed on Type X zeolite with a variety of dual metal exchange ions, e.g., LiNaX, etc., but no suggestion that naphthalene could be separated from a commercially-available feedstock or with LiX was made.
The invention herein can be practiced in fixed or moving adsorbent bed systems, but the preferred system for this separation is a countercurrent simulated moving bed system, such as described in Broughton U.S. Pat. No. 2,985,589, incorporated herein by reference. Cyclic advancement of the input and output streams can be accomplished by a manifolding system, which are also known, e.g., by rotary disc valves shown in U.S. Pat. Nos. 3,040,777 and 3,422,848. Equipment utilizing these principles are familiar, in sizes ranging from pilot plant scale (deRosset U.S. Pat. No. 3,706,812) to commercial scale in flow rates from a few cc per hour to many thousands of gallons per hour.
The functions and properties of adsorbents and desorbents in the chromatographic separation of liquid components are well known, but for reference thereto, Zinnen et al U.S. Pat. No. 4,642,397 is incorporated herein.
We have found a specific adsorbent which, in combination with certain desorbent liquids, will selectively adsorb naphthalene from a coal tar distillate feedstock containing naphthalene, substituted monocyclic aromatic compounds (including dicyclic compounds, such as indan) and paraffins.